This retrospective observational study analyzed Murmuras app data from 1074 participants in 2022 to examine demographic differences in smartphone use and nocturnal smartphone inactivity duration (a proxy for sleep-related behavior). Nighttime smartphone use increased, especially for social media and entertainment, and usage patterns varied by gender, age, education, and employment status. Most demographic groups showed no significant correlation between usage duration and nocturnal inactivity, although some subgroups showed correlations in either direction. The authors frame excessive nighttime smartphone use as potentially adverse for sleep and link this behavioral exposure to electromagnetic fields with sleep health risks.